Development of nanofiltration hollow fibers by layer-by-layer deposition of polyelectrolytes

Water hardness is one of the common issues in many countries due to presence of calcium, Ca 2+ and magnesium, Mg 2+. This work presents optimization of layer-by-layer multilayer polyelectrolyte films for water softening. Lumen deposition method was proposed to prepare two bilayers polyelectrolyte layers of PEM and compared with those use of the shell deposition membranes. Lumen deposition was done by suction of polyelectrolyte solution throughout fibers lumen using syringe. The polyelectrolytes used in experiments include poly(styrenesulfonate) (PSS), poly(allylamine hydrochloride) (PAH), poly(ethyleneimine) (PEI) and poly(diallyldimethylammonium chloride) (PDADMAC). Because of the pressure induced during lumen deposition, more compact and uniform polyelectrolyte layers were formed resulting membrane of 1nm average pore diameter, which is 50% smaller than that of shell deposition membranes. Hence, lumen deposited membranes showed better cations rejection performance with 6% Na + rejection, 96% Mg 2+ rejection and 85% Ca 2+ rejection but reduced solution fluxes at 9 LMH/bar. The rejection performance for lumen deposited membranes were independent on type of poly-cation used while PAH solution used in the lumen deposition was suggested to be within the pH range of 2-6.5 and further pH increment was not favourable. 70K PSS was recommended in nanofiltration experiments while 500K PSS may not be the best choice in terms of flux. Furthermore, lumen deposition method can be applied along with marginal effect on most of the substrate along with 99% Mg 2+ rejection. In short, the relatively high fluxes and ion rejections of lumen deposited membranes make them potentially desirable for water softening.Bachelor of Engineering (Environmental Engineering